Understanding Cycles of ConcentrationEvaporative systems are more complex to treat than closed systems. Why? It’s because the solid impurities become increasingly concentrated in the system water during the normal course of operation. Makeup impurities do not typically concentrate in closed systems. In evaporative systems, large quantities of water are used on an ongoing basis. Economics dictate the use of chemicals that can be applied at low dosages. Closed systems normally use only the amount of water required to fill the system one time and any water losses from leaks and repairs.